One of the challenges in polymer electrolyte membrane fuel cells (PEMFCs) is developing cost‐effective, active and stable catalyst for oxygen reduction reaction (ORR). Platinum alloy‐based catalyst materials have drawn great attention and been intensively investigated for the excellent activity property, with some of them already exceeding 2020 DOE target for the ORR activity. In the meantime, the electrochemical stability of these Pt alloys remains a challenge to be overcome. This review first highlights important understandings of ORR pathways and mechanisms and then proceeds to summarize recent research progresses on development of Pt alloy catalyst materials. Current obstacles in Pt alloy catalyst research are discussed, with the stability issue being specifically emphasized and a theoretical model being developed for depicting the stability property. This review also provides perspectives of future research directions in this field.

Active sites play an essential role in heterogeneous catalysis and largely determine the reaction properties. Yet identification and study of the active sites remain challenging owing to their dynamic behaviors during catalysis process and issues with current characterization techniques. This article provides a short review of research progresses in active sites of metal and metal oxide catalysts, which covers the past achievements, current research status, and perspectives in this research field. In particular, the concepts and theories of active sites are introduced. Major experimental and computational approaches that are used in active site study are summarized, with their applications and limitations being discussed. An outlook of future research direction in both experimental and computational catalysis research is provided.